Signal reproducing apparatus



Feb. 27, 1945. c. R. MINER 2,370,564

SIGNAL REPRODUCING APPARATUS Filed Dec. '24, 1943 I SIGNAL REPRODUCER I SIGNAL REPRODUCER Inventor ar foll R. Miner,

c y W His Attorney.

Patented Feb. 27, 1945 SIGNAL REPBDDUCING APPARATUS ca-mu a. Miner, Stratlord, Conn., minor to General Electric Company, a corporation of New York Application December 24, 1943, Serial No. 515,499 7 Claims. (01. ire-100.11)

* My invention relates to electric signal receiving and reproducing apparatus, more particu-v larly to combination radio and phonograph receiving and reproducing apparatus, and has for its principal object the provision of a simplified and inexpensive, but none the less reliable; discriminatory and sensitive apparatus of the character described.

Heretofore it has been common practice in combination radio and phonograph receiving and reproducing sets of relatively expensive design to provide a volume control resistor which may be selectably switched to connection either with the phonograph pick-up or with the radio receiving apparatus. Such switching apparatus constitutes an element of complication and cost which is desirably eliminated in less expensive sets. According to my invention, a permanent connection for the phonograph pick-up is provided and switching is avoided without introducing excessive loading of the phonograph signal or objectionable interference by the radio signal during phonograph reproduction. The nature of my invention and the mode of its operation will be more fully understood and its objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing, in which Fig. 1 is a schematic circuit diagram of a combined radio and phonomu triode type, known commercially as the GSQ'I.

It will of course be understood that the dis- Y charge device I 8 need not be of the combined diode and triode type, but that the diode and triode sections may suitably be sealed in separate evacuated envelopes. The discharge device I8 comprises a cathode I9 and a, first anode constituting a diode section, and a second anode 2| and control grid 22 constituting with the cathode I! a triode section. The diode section of the discharge device I8 is connected asa detector in the manner described above, and the triodesection is connected, as a signal amplifier, as will be more fully described hereinafter.- The output of the amplifying section of the discharge device It is impressed upon a suitable load resistor 23, and through a blocking condenser 24 to the control electrode or grid of a second stage of signal amplification comprising an electron discharge device 25. The control electrode of the discharge device 25 is connected to ground through a suitable grid leak resistor 25a, and the output current of the device is supplied to a suitable signal reproducing apparatus 26, such as a loud speaker, headphones, a cathode ray graph signal reproducing apparatus embodying U my invention in one form, and Fig. 2 is a. similar circuit diagram showing another embodiment of my invention.

Referring now to the drawing, and particularly to Fig. 1, I have shown an electron discharge device In as representative of a suitable source of signal modulated electric oscillations.

By way of example, the discharge device It) may be the last intermediate frequency amplifier of a radio receiving apparatus of the superheterodyne type arranged to receive amplitude modulated carrier waves. The cathode of the discharge device It! isgrounded and the anode is connected through a tuned primary winding ll of a' transformer i2 to a suitable source of unidirectional current supply indicated at B. Such a supply source may be a battery having its negative terminal grounded. A tuned secondary winding l3 of the transformer I2 is connected to supply signal modulated oscillations to a series diode detector circuit comprising a low pass resistance-capacity filter l4, l5, IS, a diode load resistor l1 and the diode'portion of an electron discharge device I 8 of the double diode high device, or the like.

Referring now to the series diode detector circuit comprising the diode elements I9 and 20 within the'discharge device l8,,it will be observed that I have shown connected in parallel circuit relation with the diode load resistor I! a direct current blocking condenser 21 and a. volume control resistor 28 in series circuit relation. The

volume control resistor 28 is grounded at one end, as is the diode load resistor, l1, and a portion of the volume control resistor adjacent the grounded end is shunted through a base compensation network comprising a resistor 29 and a condenser 30 connected in series circuit relation. The function of ,the base compensation circuit in the reception of audible signals, such as voice, music, and the like, is'well understood by those skilled in the art. The basecompensation emphasizes the response of the. audio amplifier to low and intermediate audio frequencies as distinguished from high audio frequencies. The

volume control resistor 28- serves as a poten-' tiometer, across a selectable portion of which a signal potential of desired strength may be taken off by a sliding contact 3| and impressed through a blocking condenser 32 between the control grid 22 and cathode is of the signal amplifying triode section of the discharge device i8.. Suitable grid bias is provided for the control grid 2 2 by a bias resistor 33 connected between the control grid 22 and the grounded cathode I! of the discharge device ll.

A phonograph pick-up 34 is permanently connected, preferably, through a shielded cable 38, to an interimediate point on the volume control since that portion of the resistor 28 between this point and ground provides approximately proper loading for the phonograph signal.

' amplified in the devices I8 and 2t and reproduced If now it is desired to change to phonograph reproduction, the pholn thev usual manner.

nograph is set in operation to impress signal frequency oscillations from the pick-up 31 across the base compensation section of the volume control resistor 28. This lower section oi the volume control resistor now serves as a potentiometer, across a selectable portion oi which the phonograph signal oscillations of the desired intensity may be chosen'by the volume control slider 3| and and applied to the signal amplifyins' devices. It will oi course he understood that if, during suchv phonograph reproduction, the radio receiving apparatus is left tuned to a staresistor 28; As shown at Fig. 1, this intermediate point may suitablybe the point or connectionof the. base compensation circuit 29, Ill,

serveas separate potentiometers for the lie-- modulated signal voltage from the radio apparatus and for thesignal voltage from the phonograph apparatus. Since the radio andphonograph signal voltages appear across .entirely separate portions of the volume control resistor, they do not interfere with one another I in any way.- Thus both signals may be simultaneously impressed upon the resistor 28 and may be selectably chosen for application to the audio amplifying devices .by positioning the volume control slider 3| either above or below the grounded point of. the resistor 28.

, I'therefore wish to have it understood that I intion, a certain amount of radio interference will be encountered despite the fact that theupper section of the volume control resistor 28 provides substantial attenuation of the radio signal. Such interference may be substantially eliminated very simply by the operator merely by detuning the radioreceiver to some point between stations.

At Fig. 2 Ihave shown another embodiment my invention in which radio interference with phonograph reproduction is entirely eliminated, despite the maintenance of a permanent connection between the phonograph pick-up and thevolume control resistor. Except for-the con nection to the volume control resistor, the apparatus of Fig. 2 is entirely similar to that of Fig. 1 and like parts have been assigned the same reference numeral. It will be noted that at Fig.

2 the volume control resistor is grounded at an intermediate point, rather than at one end, and

that the radio signal is impressed across that section of the resistor 28 between the grounded Point and the upperterminal, while the phonograph signal i impressed across an entirely separate section of, the' resi'stor 28 between the grounded polntand the opposite terminal of the I resistor. To provide proper loading for the signal fromthe phonograph pick-up 34', a condenser 38 in serles-witha resistor 31 is shunted across the phonograph section of the resistor 2i. lhe value of condenser-'and resistor should be chosen to provide the mqdfl pleasing frequency characteristic; for phonograph reception.

In the operation or the apparatus shown in Fig. 2, it will be evidentthatlthe adjacent sections or the volume control resistor 28 on opposite sides of the grounded intermediate point 76 tend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention. 1

What I claim as new and desire to secure by Letters Patent of th Unit'ed .States is:

'1; A combination radio-phonograph receiving and reproducing apparatus comprising a source of signal modulated electric oscillations, a resistor, means for deriving from said source and impressing across at least a portion of said re sistor oscillation at signal frequency in accordance with said signal modulation, is phonograph pick-up permanently connected to said resistor for impressing other signal oscillations across a portion of said resistor, and means'variably responsive to the signal oscillations appearing across selectable portions of said resistor for reproducing said signals.

' 2. A combination radio-phonograph receiving and reproducing apparatus comprising a source of signal modulated electric oscillations, a resistor having one end permanently connected to a point of fixed potential, means for deriving from said source and impressing across said resistor oscillations at signal frequency in accordance with said signal modulation, a phonograph pickup permanently connected across a portion'oi said resistor including said point of fixed potential to impress across said portion other signal oscillations, and means variably responsive to the signal oscillations appearing across selectable portionsv of said resistor for reproducing said signals.

3. A radio-phonograph receiving and reproducing apparatus comprising a source of signal modulated electric oscillations, a volume control resistor, means for deriving from said source and impressing across said resistor oscillations at signal frequency in accordance with said signal modulation, a phonograph pick-up permanently connected to an intermediate point on said resistor for impressing other signal oscillations across a portion or said resistor, said portion of a said resistor providing maximum attenuation of .said first signal oscillations, and means variably responsive to the signal oscillations across selectable portions of said resistor including said portion of maximum attenuation for reproducing said s als.

4. A combination radio-phonograph receivin and reproducing apparatus-comprising a source of signal modulated electric oscillations, a volurne control resistor having one end connected to a point of predetermined fixed potential, a base compensation network connected between said 7 point 01' fixed potential and an intermediate point on said resistor, mean; for deriving -trom sfil aerate;

. source and impressing across said resistor oscillations at'signal frequency in accordance with said ignal modulation, 9. phonograph pick-up permanently connected to said intermediate point of said resistor tor impressing other signal oscillations between said intermediate point and said point of fixed potential, and means variably responsive to signal oscillations between said point of-fixed potential and selectable points on said resistor for reproducing said signals.

5. A combination radio-phonograph receiving 1 and reproducing apparatus comprising a source from said source and impressing across a first portion of said resistor including said intermediate point oscillations at signal frequency in ac-' cordance with said signal modulation, a phonograph pick-up permanently connected to impress other signal oscillations across a second portion of said resistor including said'intermediate point,

' and means variably responsive to signal oscillapermanently connected to impress other signal oscillations across a second portion oisaid resistor, and means variably responsive to signal oscillations appearing across said portions or said resistor selectably' to'reproduce said signals.

6; A combination radio-phonograph receiving and reproducing apparatus comprising a source. oi, signal modulated electric oscillations, 9. vol- 'ume control resistor having an intermediate point permanently connected to a point or predetermined fined potential, means for deriving tions between selectable points on said resistor and said intermediate point for reproducing said 7 signals. v

7. A combination radio-phonograph receiving and reproducingapparatus comprising a source of signal modulated .electric oscillations, a volume control resistor having a, point of predetermined fixed potential, means for deriving from said source and impressing across at least a portion or said resistor including said oint or fixed potential oscillations at signal frequency in accordance with said signal modulation, a phonograph pick-up permanently connected to impress other signal oscillations across a portion of said resistor including said point of fixed potential,

and means variably responsive to signal oscillations between said point' oi fixed potential and selectable points on said resistor to: reproducing said signals. a omnonn, a. L i 

